Classes within a Subject can be renamed. Class names are not visible to students.
On the Students page, select the Class you want to rename from the list on the left side of the screen, click Rename class and enter the new name. Keep it short - this will appear in various places across Stile including the Available to column of the Lessons page, the Markbook, and your Teach and Analyse pages of each activity.
You may also be interested in the following resources: